Standard primary flight control systems are generally reliable. Aircraft designers have successfully integrated complex mechanical and electrically controlled flight control components into these standard primary flight control systems. Such systems rely upon aircraft flight surfaces e.g. rudders, flaps ailerons, to control the heading and pitch of an aircraft.
Many standard primary flight control systems have redundant components as part of the standard primary flight control backup system. In the rare event that system fails however, a backup flight control system should be used that is not integral to the primary flight control system. One such flight control system is based entirely on control of the engine thrust.
For multi-engine aircraft, one previously disclosed method of controlling the aircraft uses engine thrust to control the aircraft pitch angle and roll. Pitch angle is controlled by concurrent equivalent thrust adjustments upon laterally positioned engines. Aircraft banking is controlled by differential thrust adjustments upon laterally positioned engines.
The use of differential engine thrust to control aircraft banking is however inexact and leads to difficulty in flying and hazardous landings. Several factors contribute to the control problems; the pilot's inexperience with this method of aircraft control, the less exact control method augmented by a sluggishly responding differential engine control, and the stress of an emergency situation.
One example of related art disclosed in the art of engines-only flight control uses static control parameters to generate servo command parameters indicative of the desired flightpath. For instance U.S. Pat. No. 5,330,131 issued to Burcham et al. ("Burcham") discloses an engines-only flight control system based on differential engine thrust. The disclosure in the Burcham patent discloses a pilot controlled input device consisting of either a control stick, thumbwheel or radio frequency receiver. The input device generates command parameters that are then modulated by scaling circuits and amplified by static gains. The outputs from the static gain amplifiers are then applied to the left and right engine servos through a summation function. The Burcham invention therefore discloses a successful system of engines only flight control. However, it is the static control parameters that lead to sluggish and unfamiliar aircraft banking response.
Another example of remotely related art is disclosed in U.S. Pat. No. 5,551,402 issued to Dahl ("Dahl"). Dahl's system discloses the use of wireless transmitters to control the flight control surfaces by the use of receivers positioned within, or on, the engines. However, Dahl's system of backup flight control depends upon the use of wireless transmitters and receivers, rather than differential engine thrust, to replace the primary engine flight control system.
Therefore, in the event that the standard primary flight control components fail to respond to a pilot's stick commands, a backup engines-only flight control system should be used that does not utilize the standard flight control components, but still permits banking and pitch adjustments. Moreover, this backup engine-only-flight-control-system should preferably respond in a manner that is substantially similar to what the pilot would expect from the primary flight control system. The present invention accomplishes these aims by the incorporation of lead compensation to backup engines-only flight control systems by use of a lead controller. Therefore, the present invention improves the responsiveness and predictability of engines-only flight control, thereby improving the usability, safety and reliability of engines-only flight control.